Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister coupled to the fuel tank which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon fuel vapor.
The fuel tank may be further coupled to a vapor recovery line (vapor recirculation line). The vapor recovery line may be configured to circulate and/or hold a percentage of refueling vapors, thus limiting the rate of fuel vapor canister loading. Fuel vapors may recirculate back to the fuel tank via flowing through the recirculation line and through a filler neck of the fuel tank. Further, depending on the fuel dispenser, the fuel vapors within the vapor recovery line may be returned to the fuel dispenser, thus limiting the total fuel vapor stored within the fuel vapor canister for a given refueling event. By reducing canister loading during refueling events, the canister sizing may be reduced, which may reduce costs and weight associated with the vehicle.
Fuel vapor recirculation lines include orifices to regulate the fuel vapor flow rate through the recirculation line. In many examples, such an orifice comprises a fixed orifice that is set manually via a technician. The size of such an orifice may be configured so as to maximize vapor recirculation without resulting in fuel vapors (e.g. hydrocarbons) exiting to atmosphere via an inlet at the fuel filler neck. However, such orifices of fixed size may not be robust to variability in flow rates of fuel from various fuel dispensers. For example, different fuel stations may have inherent variability in fuel flow rates (e.g. gallons per minute, or GPM). Such variability may result in canister loading of fuel vapors to a greater extent than desired under some circumstances, while resulting in the release of undesired evaporative emissions (e.g. hydrocarbons) to atmosphere via the inlet at the fuel filler neck under other circumstances.
To address such issues, a variable orifice (also referred to herein as a variable orifice valve, recirculation valve, or variable orifice recirculation valve), may be installed in the recirculation line. Such a variable orifice may include an orifice that changes in size as a function of fuel station pump dispense rate. For example, at higher refueling rates it is desirable to re-route a greater amount of fuel vapors to the fuel tank rather than to the canister, thus the variable orifice may open to a greater extent under such conditions. Alternatively, at lower refueling rates it is desirable to re-route a lesser amount of fuel vapors to the fuel tank, thus the variable orifice may close to a greater extent under such conditions.
However, as the variable orifice ages, the variable orifice may stick in one of an open or closed configuration. As an example, a stuck closed variable orifice may result in an undesirable increase in canister loading. In another example where the variable orifice is stuck open, an increase in release of undesired evaporative emissions to atmosphere via the fuel filler neck inlet may result.
Diagnosing whether the variable orifice valve is stuck in one of an open or closed configuration is challenging. The inventors herein have recognized these issues, and have herein developed systems and methods to at least partially address them. In one example, a method for a vehicle comprises, during a refueling event, in response to a first inferred fuel fill rate, diagnosing whether a variable orifice positioned in a fuel vapor recovery line is stuck in a first state, and in response to a second inferred fuel fill rate, diagnosing whether the variable orifice is stuck in a second state including diagnosing the first state and the second state based on an estimated fuel system pressure. In this way, based on a fuel fill rate, by comparing fuel system pressure to an expected pressure, a stuck open or a stuck closed recirculation line orifice may be diagnosed.
In one example, fuel system pressure during refueling at different fuel fill rates may be stored in the controller database as look-up tables. During lower fuel fill rates (such as lower than a threshold), diagnostics for a variable orifice stuck in an open position may be opportunistically carried out, while during higher fuel fill rates (such as higher than a threshold), diagnostics for a variable orifice stuck in a closed position may be opportunistically carried out. During the diagnostics, fuel system pressure may be monitored via a fuel tank pressure transducer (FTPT) and compared to a threshold pressure corresponding to the current fuel fill rate, as retrieved from the look-up tables. If during lower fuel fill rates, the fuel system pressure is lower than the corresponding threshold pressure, it may be inferred that the recirculation line variable orifice may be stuck in an open position. Similarly, if during higher fuel fill rates, the fuel system pressure is higher than the corresponding threshold pressure, it may be inferred that the recirculation line variable orifice may be stuck in a closed position.
In this way, by opportunistically diagnosing the variable orifice at different fuel fill rates, it may be possible to indicate if the variable orifice is stuck in an open position or in a closed position. By using the FTPT sensor for variable orifice diagnostics, additional hardware may not be engaged. The technical effect of diagnosing degradation of the recirculation line variable orifice is that suitable mitigation actions may be undertaken to reduce the possibility of fuel vapor system canister overloading or undesired fuel vapors escaping to the atmosphere via the fuel filler neck inlet. Overall, by monitoring the health of the fuel recirculation line variable orifice, emissions quality may be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.